(1) Field of the Invention
The present invention relates to the wrapping of sheet material around cardboard or similar flat material to form an overlay. More specifically, the present invention is directed to apparatus for wrapping an overlay around the leading, trailing and side edges of a flat member such as, for example, the cardboard which may define the cover of a book. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in the wrapping of overlay material around cardboard or similar flat materials in the manufacture of book covers. In the automatic production of book covers, it is known to wrap the overlay first around the lateral or side edges of the cover and then to subsequently wrap the overlay around the leading and trailing edges of the covers. In the prior art, in order to accomplish the lateral wrapping, the overlay material is laminated to the cardboard with the overlay extending past the edges of the cardboard, the laminate is advanced and gripped by feed chains and is thereafter raised upwardly at an angle of 90.degree.. The overlay is then forced around the edges of the cardboard by inward moving wrapping shafts which travel with the covers. In the prior art apparatus, rotatably mounted wrapping fingers, arranged in a side-by-side relationship, are located across the direction of travel above the plane of motion of the covers for the purpose of folding the overlay around the leading edge. These wrapping fingers are bent at right angles opposite to the direction of travel and, in the ready position, press against a hold down shaft. Thus, the cover will run into the wrapping fingers and, when it overcomes the force of a spring bias thereon, will push the fingers out of the plane of motion. The overlay material is wrapped around the cardboard by the motion of the fingers as they pass over the leading edge of the cover. The trailing edge wrapping in the prior art apparatus is accomplished in the same manner but with wrapping fingers which are transported for a brief period with a considerable higher velocity than the speed of advance of the cover whereby the rear edge wrapping fingers force the overlay material around the cardboard upon overtaking the cover. A catch mechanism is required in order to avoid an extra displacement of the cover in the direction of travel when it is overtaken by the rear edge wrapping fingers.
Previously known methods and apparatus for the wrapping of overlay material around cardboard, the prior art apparatus briefly described above, for example, has not provided a completely satisfactory product. A first deficiency with the prior art apparatus resides in the fact that it is virtually impossible to apply adequate and even pressure to the overlay because of the relatively rapid sliding of the wrapping fingers around the edges of the cardboard and over the glueing area near the edges.
The clamping of the overlay to the cardboard for a significant period of time, the length of which depends on the type of adhesive used and also upon its coating thickness, is a factor which has not been taken into account in the design of prior automatic cover forming equipment. In order to achieve the requisite permanent adhesion of the overlay to the cover, the setting time of the glue is of particular importance. This is particularly critical when using comparatively stiff overlay materials such as Balacron, Skiveitx etc. As a result of the short period of time in which pressure is applied to urge the overlay against to cover in prior art equipment, the overlay often separates from the cardboard. This, of course, will lead to rejection of the cover.
Because of the exertion of only small clamping forces on the edges and on those areas of the covers immediately adjacent the edges, prior art automatic cover forming apparatus has been generally incapable of achieving a tight wrapping of the overlay around the cardboard; this being particularly true when comparatively stiff overlay materials are employed. The problem is not solved by increasing the applied pressure since this will invariably result in damage to the overlay and an unacceptable product. Thus, the well defined edges desired for book covers cannot be achieved using prior art wrapping systems and apparatus.
A further problem which has plagued prior art techniques, and which is attributable to the inability to obtain a tight wrapping, is the entrapment of air between the overlay and the cardboard and/or the production of covers having hollow edges.
As an additional deficiency of the prior art, because of the design of previously available automatic cover forming machines, a relatively short time is available for the clamping process and thus increases in production rate have not been possible.